Headlight tester



P 1944- I H. e. HQLMES 2,358,010

HEADLIGHT TESTER Filed March 3, 1941 5 Sheets-Sheet l v INVENTOR -HERBERT 6. HOLMES ATT OR N EY Sept. 12, 1944. H, G. HOLMES 2,358,010

HEADLIGHT TESTER Filed March 5, 1941 5 Sheets-Sheet 2 FII3 4E INVENTOR HERBERT 6. HOLMES ATTORNEY Sept. 12, 1944. H. G. HOLMES HEADLIGHT TESTER 5 Sheets-Sheet 3 Filed March 5 F IEI-LEL f 7 7 llllfllnrldVl /dll/llllllllllllg M W W i ATTORNEY HEADLIGHT TESTER Fild March 3, 1941 5 Sheets-Sheet 4 ATTORNEY P 1944- H. G. HOLMES v 2,358,010

HEADLIGHT I,TESTER Filed March 3, 1941 5 Sheets-Sheet 5 4 A F I|3 1 INVENTOR HERBERT 6. HOLMES ATTORNEY "Patented Sept. 12, 1944 UNITED STATES PATENT OFFICE HEADLIGHT TESTER Herbert G. Holmes, Lansing, Mich, assignor to Food Machinery Corporation, San Jose, Caiii., a corporation of Delaware Application March 3, 1941, Serial No. 381,455

9Claims.

This invention relates to apparatus for testing the headlights of automotive vehicles.

It is periodically necessary to test the headlights of automobiles to determine whether they conform to certain requirements enforced by law for the public safety on the highway. The factors to be determined are the intensity of the light emitted by each lamp, and the aim of its beam, as measured by the vertical and horizontal inclinations of the beam direction to the line of travel of the vehicle.

The principal object of this invention is to provide improved apparatus for determining the aim of the headlight beam, as well as its intensity.

It is an object to provide an instrument adapted to be placed in the beam and to indicate when the longitudinal axis of the instrument is aligned with the rays of the beam whereby the-instrument axis will represent the directional line of the beam.

Another object is to provide means to facilitate the positioning of the instrument axis in alignment with the beam so that the headlights may be tested quickly and accurately.

Another object is to provide an instrument having a light-sensitive cell with a means for directing rays from the beam onto the cell which is accurate in operation and susceptible of emcient and economical manufacture.

Another object is to provide a visual means for focusing the rays on the light-sensitive cell to facilitate rapid adjustment of the instrument and to serve as asafety check in the use of the instriunent.

Other objects will appear after the disclosure of an apparatus in which the invention has been embodied.

In the drawings:

Fig. 1 is a plan view of the headlight testing instrument.

Fig. 2 is a front elevation thereof.

Fig. 3 is a front elevation of the light-sensitive cell which is located within the instrument.

Fig. 4 is a section of the cell taken as indicate by the arrows 4-4 in Fig. 3.

Fig. 5 is a vertical section through the longitudinal axis of the instrument.

Fig. 6 i a side elevation of the stand with the instrument in place thereon.

Fig. 10 is a horizontal section taken as indicated by the arrows Ill-l 0 in Fig. 9.

Fig. 11 is a fragmentary vertical section taken as indicated by the arrows l l-l l in Fig. 9.

Fig. 12 is a plan view of an automobile in position for testing its headlights by means of the apparatus.

Fig. 13 is a side elevation of the same.

Figs. 14 and 15 are detail views of instrumentalities employed in determining the line of travel of the automobile, Fig. 14 showing a device attached to the side of the vehicle and Fig. 15 showing a stand which is placed on the ground alongside the vehicle.

The headlight testing instrument comprises a box-like case (Fig. 1) having handles 2|, 22 attached to the left and right side walls 23 and 24, respectively. A post 26 projects forwardly from the front end of the instrument.

As shown in Fig. 5, the post 26 has a rubber button 21 in the forward end, which, under certain conditions of operation later to be described, is brought into contact with the lens of the headlight. The post 26 extends rearwardly through a rubber bushing 22 fitted in a central aperture 29 of a glass plate 30, which is attached by means of screws ii to the front wall 32 of the case 20. The glass plate is circular in shape and serves as a window for the large circular aperture 33 (Figs. 2 and 5) in the front wall 32 through which light from the headlight beam enters the instrument.

Behind the glass plate 30 is a diaphragm 3! which is rigidly mounted in the case 20 by attachment to lugs such as 36, 31 by screws 38, 28. The lugs 36. 31 are formed integrally with the side wall 23 of the case. A similar pair of lugs is formed on the right side wall 24 for attaching the right side of the diaphragm 35 thereto. The mounting lugs in the case serve to accurately position the diaphragm 35 so that it lies in a Plane perpendicular to the longitudinal axis of the instrument. The post 26 is attached to the diaphragm 35 by means of a screw ti and is located with its axis coincident with the longitudinal axis 40.

. A light-sensitive cell 80 is mounted on the rear side of the diaphragm 35 by means of spacers Ii threaded to receive screws 52 and II which pass through the base of the cell and the diaphragm, respectively. The cell is of the dry disc type which is self-generating in that when exposed to light an electromotive force is generated between the plates of the cell which can be measured with a suitable meter. The

and 59 (Fig. 4), and these terminals are connected by suitable wiring (not shown) to a microammeter 51 (Fig. 1) having a scale 59 and pointer 59. A translucent glass plate 60 (Fig. 4) is employed as the window of the cell 50. On account of the wide variation in output of photoelectric cells oi this type it is sometimes necessary to employ a thin sheet 60' of translucent plastic material as a filter. The plate 60 is also used as a target, and for this purpose is provided with vertical and horizontal lines BI, 62 (Fig. 3) on the front face thereof 'which indicate the center of the target and cell by their intersection 63. The point 93 is located on the longitudinal axis 40 (Fig. 5). The target 60 is visible to the operator through a' window 64 in the top of the case 20.

Means are provided for selecting rays from the headlight beam and focusing them on the with aplurality of apertures as shown in Fig. 2

' for admitting light rays from selected portions of the headlight beam. These comprise two horizontal slots 65, two vertical slots 66 and a plurality of round apertures 61 disposed as shown in the spaces between the slots. At the rear of the instrument a second diaphragm (Fig. 5) is rigidly mounted in the case 20 by attachment to lugs such as 1|, 12 formed in the side walls. The rear diaphragm 10 is provided with apertures identical to the apertures in the front diaphragm 95, and the diaphragm 10 is mounted so that its apertures are in longitudinal alignment with the apertures of the front diaphragm. By this arrangement light rays passing through the apertures of diaphragm 95 and which are at least approximately parallel. to the longitudinal axis 40 of the instrument may pass through the rear apertures to light collecting means, preferably a concave mirror 15, while a large percentage of angular rays which tend to difiuse the light incident upon the mirror are cut off. The only difference between the two diaphragms is that the rear diaphragm is concave.

The concave mirror 15 is mounted behind the rear diaphragm 10 by means of mounting members 16 which are suitably formed at 11 to receive the edge of the mirror 15 and are attached to the rim of the diaphragm 10 by means of screws 19. The curvature of the mirror 15 is such that the center 63 of the target 90 is the focal point of the mirror, and the axis of the mirror 19 is coincident with the longitudinal axis 40. It will also be observed that the light rays of the headlight beam which reach the is as follows: The operator supports the instrument in his hands by grasping the handles 2|, 22 (Fig. 1) He presses the rubber button 21 into contact with the center of the headlight lens. The instrument is now disposed in the path of the beam so that the light will enter the instrument through the window 30 in the front wall thereof. Rays such as 19, 90 which pass through aligned apertures in the front and rear diaphragms 95, 10, respectively, strike the mirror 10 and are reflected thereby to the target 00.

which is visible to the operator through th window 94.

Maintaining the rubber button 21 in engagement with the headlight lens the operator moves the instrument back and forth and up and down, as he observes the meter 91. When the longitudinal axis 40 is in alignment with the beam of the headlight, the rays of the beam will pass through the diaphragms parallel to the axis 40 and will be focused on the target 90 by the mirror 15. This condition is indicated to the operator by the maximum reading on the meter 51. The scale 59 of the meter 51 is calibrated in candlepower so that the maximum readin thereon indicates the intensity of light emitted by the headlight and the operator can thus observe whether it is within the required limits.

The vertical aim of the headlight beam is determined by mechanism which measures the angle of inclination of the instrument axis 40 to the horizontal. A spirit level 92 (Fig. 5) is rigidly mounted on the upper end of a lever 99 which is mounted on a pivot 94 in a fixed bracket 95 rigidly mounted on the side wall 23 of the case by means of posts 89, 91. The lower end of the lever 83 is connected at 98 to a pointer 09 which oscillates on a pivot 90. The tip 9| of the pointer moves over a scale 92 (Fig. 1). The

spirit level 92 is disposed adjacent the scale 92 and has the usual bubble 93 which when centered between the lines 94, 95 is an indication that the level 92 is in a true horizontal position.

The vertical aim adjusting knob 91 is disposed within the left handle 2I. The shaft 98 on which the knob is mounted extends through the side wall 23 into the interior of the case where it has secured thereon a pinion 99 (Fig. 5). A rack I00 is actuated by the pinion 99 and is an integral Part of the light received on the target 60 is I transmitted to the cell 50 and part of it is reflected to form an image of the spot of light part of a link which is connected at IN to the pointer 89. For a more detailed disclosure of the vertical aim mechanism reference is to be had to my application Serial No. 341,178, filed June 19,1940.

The operation of the vertical aim measuring device is as follows: When the longitudinal axis 40 of the instrument is in a true horizontal position and the knob 91 is adjusted to center the bubble 93 in the spirit level 92, the pointer 9| will be opposite the zero point on the scale 92 and opposite the bubble 99 and intermediate the index lines 94, 95. When. the instrument axis 40 is inclined to the horizontal and the knob 91 is turned to center the bubble 99, the pointer 91 will be removed from its central position an amount indicated by the scale 92. The scale 92 is graduated to indicate the elevation of the beam above or below the horizontal in inches at a distance of twenty-five feet from the headlight.

The operator may determine the vertical aim of the headlight while holding the instrument 'with its longitudinal axis in line with the beam direction as previously explained, by adjusting the vertical aim knob with his left thumb to center the bubble 99 between the index lines 94, 95, and thereafter reading the scale 92.

In order to determine the horizontal aim, as well as the vertical aim, I provide apparatus, including a stand for supporting the instrument, which will now be described. As shown in Fig. 6, the instrument is mounted on a stand adapted to run on a track I02 (Fig. 12) which-has parallel rails I03, I04. Flanged rollers I05, I06 (Fig. 9) engage the rail I04 and a roller I01 (Figs. 6 and 9) engages the rail I09. The three rollers I05,

I08, I01 are suitably mounted in the base IIO of the stand. Two parallel columns III and-I I2 (Fig. 9) are rigidly secured at their lower ends in the base H and rise vertically therefrom.

The upper ends of the columns are interconnected by means of a yoke casting I I3.

A support indicated generally at I (Figs. and 9) is vertically adjustable on the columns III and H2. The support I20 has two bearing portions I2I, I22 which provide sliding bearings .for the support I20 on the columns III, H2.

The bearing portions I2I, I22 are interconnected by a transverse web I23 cast integrally therewith. Extending forwardly from the web I23 and cast integrally therewith is an arm I24.

The horizontal aim bar I25 (Fig. 6) is mounted.

on the arm I24 for swinging movement in a horizontal plane by means of a vertical pivot I28. As shown in detail in Fig. 11, a boss I21 is formed in the front end of the arm I24. This boss has a vertical bore I28 and a counterbore I29. The pivot pin I30 fits in the bore I28 and is riveted to the horizontal aim bar I25 at I3I. The lower end of the pivot pin I30 is threaded to receive a nut I32- A compression spring I33 is interposed between the nut and the shoulder of the counterbore I29. The pivot pin I30 which is rigidly attached to the bar I25 is free to rotate in the bore I28 and the spring I33 holds the under side of the. bar I25 against the upper face I34 of the boss I21. 3

The rear end of the horizontal aim bar-I25 (Fig. 6) rests upon an upstanding rib I35, formed on the web I23 of the support I20,- and is free to slide back and forth thereon as the bar turns about its pivot I25. A handle I40 for swinging the bar I25 is rigidly attached thereto at I. As shown in Fig. 10, the handle I40 has a window I42 therein provided with a cross hair I43 for indicating the position of the horizontal aim bar relative to an arcuate scale I44. A ledge I formed integrally with the support I20 and proinstrument and its support vertically on the col- J'ecting rearwardly from the web I23 (Fig. 6)

supports the scale I44. For a purpose hereinafter explained, the scale I44 is made adjustable. It is attached to the ledge I45 by screws I45 (Fig. 6) and I41 (Fig. 10) provided with knurled clamping nuts. The screws pass through short arcuate slots, such as I48, formed in each end of the scale. When the nuts are loosened the scale can be adiusted by shifting it laterally and the adjustment can then be maintained by tightening the nuts.

The instrument supporting bar I (Fig. 6) is attached to the forward end of the horizontal aim bar I25 by means of a spring steel strap I5I which acts as a hinge. As shown in Figs. 10 and 11, the strap I5I is secured to the bar I50 by rivets I52 and tothe bar I25 by rivets I53. Riveted to the bar I50 is a dowel pin I54. The rear end of the supporting bar I 50 (Fig. 10) has a threaded aperture I which receives an adjusting set screw I50 (Fig. 6) which bears against the horizontal aim bar I25. Turning of the adjusting screw I 80 causes the supporting bar I50 to rock on its hinge I5I.

The headlight testing instrument previously described is adapted to be detachably mounted on the supporting bar I50 in a predetermined position. A supporting bracket I52 (Fig. 6) is rigidly secured to the under side of the bar I50. This bracket has laterally extending wings I53 (Figs. 9 and 10). The instrument is supported by the bar I50 and the wings I53. It is fixed in a predewhich the plate encompasses.

termined position thereon by means of dowel 16 pins. The front dowel pin I54 (Fig. 11) has already been referred to. The rear dowel pin I54 (Figs. 6 and 10) is rigidly secured in the bar I50 above the bracket I52. As shown in Fig. 5, the I tures I55, I51 (Fig. 5), the instrument is secured. in place by a set screw I58 (Figs. 6 and 10) threaded through a post I59 which is rigidly mounted on the bar I50. When the set screw I58 fis tightened the instrument is shifted forwardly on the bar I50 to engage the rear edges of the aprturesi55, I51 (Fig. 5) under the shoulders I54, I54 on the dowel pins.

Means are provided to facilitate adjusting the umns III, II2 of the stand. To counterbalance the weight of the instrumentand the support I28 (Fig. 9) a spring wound reel I10 is rotatably mounted in the yoke H3 at the top of the stand. A tape "I attached to the reel, and wound thereon isconnected at I12 to the support I20. This enables the support I20 to be readily and easily slid up and down on the columns III, I I2.

In order to permit the operator to obtain fine adjustments the device shown in detail in Figs. 7 and 8 is provided. Formed integrally with the bearing portion I2I of the support I20 is an enclosure I15 having an upper wall I15 and a lower wall I11. This enclosure is open at the rear to permit the entrance of a jaw I18 formed on a lever I80. The lever I has a hub I8I bored to receive a pin I82 which is supported in cars I83, I84 formed integrally with the support I20.

The jaw I18 of the lever I50'enters a notch I85 (Fig. 7) formed in-a plate I85 and is adapted to engage the plate on itstop or bottom depending on whether the lever I80 isturned clockwise or.

counterclockwise, respectively, on its pivot I82 (Fi 8). which is larger in diameter than the column II I A compression spring I89 is interposed between the plate I88 and the upper wall I15 of the enclosure I15, and an- The plate I85 has a hole I88 therein 4 other compression spring I90 is interposed beas follows: lgormally the parts occupy the positions shown in Fig. 8 where the two springs I55, I80 maintain the plate I86 horizontal. When the lever I50 is depressed the jaw I18 is tilted and the plate I85 crimped against the column and continued depression of the lever I80 causes the support to be moved downwardly, the jaw using the plate as a fulcrum. If the support cannot be lowered as far as desiredwith one movement of the lever it is released, whereupon the springs restore the parts to normal. The lever can then be depressed again and the plate will take a fresh grip on the colunm and the support can be lowered further. Conversely, the support can be raised by lifting the lever I80, in which case the 'plate is tilted the other way. .The device is thus reversible in operation and permits very delicate adjustments of the support vertically on the columns.

In order to check the horizontal aim of the headlights I provide means for determining the line of travel of the vehicle and the relation of that line to the track. Mounted in the top of the instrument are front and rear sights 200, 20I (Fig. 6). As shown in Fig. 5, the front sight 200 is attached to the case by means of a screw and of a suction cup 2.

in the vertical plane containing the longitudinal axis 40 of the instrument and are employed to align that axis with the line of travel of the vehicle by sighting on two pointers 2I0, 2 (Fig. 13).- The pointer 2 (Fig. 14) is a pendulum rod suspended from an eye formed in the end of a supporting rod 2 I2 which is adapted to be attached to the side 2 l3 of the automobile by means The rod 2I2 is bent -downwardly and inwardly. The lower end is encased in rubber tubing 2I5 for contact with the side The pointer 2I0 (Fig. 15) is slidably received and frictionally held in a vertical tube 2I6 comprising part of a portable stand 2" having a base 2I0 which rests upon the floor. A sleeve 2|! is rotatably mounted on the stand 2" and 'has attached thereto a horizontally-extending arm 22! which has a rod 22I secured in its outer end. As

can be seen in Fig. 12, the rod 22I provides two pointers 222, 223 projecting perpendicularly from the arm.

The operation of testing the headlights will now be described. Theautomobile 230 (Fig. 12)' is driven up to the track I02 so that the center line of the automobile is approximately at right angles to the track, and so that there is sufficient right angles to the track, it is necessary to swing the horizontal aim bar I25 (Fig. 10) by means of th handle I40 in order to bring the instrument sights into line with the pointers. After alignment of the sights the horizontal aim scale I44 is adjusted by loosening the nuts on the screws I45, I41 to bring the zero mark of the scale under the cross hair I43. Then the nuts are tightened to hold the scale in adjusted position. In'this man ner the angular relationship between the line of travel of the automobile and the track is determined and maintained throughout the test.

The stand is then rolled along the track to position the instrument in front of the left-hand l headlight, as shown in broken lines at 240 in-Fig.

l2.- The instrument is adjusted to bring its longitudinal axLs 40 (Fig. 5) into line with the headlight beam where the spot of light willappear at the center of the target and the meter 51 (Fig. 1) will give its maximum reading. To so position the instrument the following adjustments are available: Horizontal translation by rolling the stand on the track. Vertical translation by moving the support I20 (Fig. 6) on the columns III, I I2, fine adjustments being obtained by operating the lever I80. Tilting in a vertical plane is efe 'fected by turning the screw I50. Swinging in a horizontal plane is obtained by operating the handle I43 to turn the bar I25 about its pivot I25.

When the instrument has been positioned in line with the beam the horizontal aim is indicated by the cross hair I43 on the scale I44. The-'vertical aim is determined, as previously explained,

clearance between the headlight tester and the Y front end of the automobile to permit the tester stand to be rolled along the track in front of the automobile. The stand 2 I1 is placed in the position shown in Figs. 12 and 13 with the pointer 222 opposite the rear hub cap 23I. The arm 220 is swung around through one hundred eighty degrees to the position indicated in dot-and-dash' lines. The automobile is rolled'backward until the rear hub cap 23I is opposite the pointer 223.

The pendulum. pointer-2H is now mounted on the side of the automobile by attaching the suction cup 2. The pendulum 2 is mounted so that it hangs directly over the pointer 2I0 in vertical alignment therewith. In this manner the point 234 of the pendulum pointer 2 is placed imaginary line'in space. If the automobile moved.

in a straight line the line of travel is represented by a line jcining'the points 234, 235. If for any reason the automobile moved along a curved path the point 234 described an arc of which, never by turning the knob 31 (Fig. 1) until the bubble 33 is centered between the marks 34, 35. The

vertical aim is then indicated by the pointer 3| on the scale 92. After the left-hand headlight has been tested the stand is rolled along the track to position the instrument in front of the righthand headlight and the procedure for testing the beam isrepe'ated.

Having thus described my invention and in what manner the. same may be used, what I claim as new and desire-to protect by Letters Patent is: 1. An apparatus for determining the direction of a headlight beam comprising a pair of diaphragms for positioning. in front of a headlight, sa d diaphragms being arranged one behind the other and provided with aligned apertures, whereby to separate parallel shafts of light from. said beam and permit the passage of said shafts there.-

through, light intensity indicating means, and a concave mirror arranged to receive said parallel shafts of light and focus them onto said intensity theless, the line 234-235'is the chord, so that for. v

the automobile does not travel in a line exactly at 76 indicating means, said diaphragms shielding said mirror and indicating means from the remaining rays of said headlight beam.

2. An apparatus for determining the direction of a headlight beam comprising a diaphragm. for

positioning in front of a headlight, a concave diaphragm arranged behind said first diaphragm, said diaphragms being provided with a plurality of aligned apertures for selecting parallel shafts oflight from said beam and permitting the passage of said shafts therethrough, light intensity indicating means, a concave mirror adjacent. said concave diaphragm arranged to receive said parallel shafts of light and focus them onto said indicating means, said diaphragms shielding said mirror and indicating means from the remaining rays of the headlight beam.

3. An apparatus for determining the direction of a. headlight beam comprising a diaphragm for positioning in front of a headlight, a concave diaphragm behind said first diaphragm, said diaphragms being provided with a plurality of aligned apertures for selecting parallel shafts of light from said beam and permitting the passage of said shafts therethrough, light intensity indicating means intermediate said diaphragms, a concave mirror behind said concave diaphragm arranged to receive said parallel shafts of light and focus them through the apertures in said concave diaphragm onto said indicating means, said diaphragms shielding said mirror and indicating means from the remaining rays of said headlight beam.

4. An apparatus for determining the direction of a headlight beam comprising means adapted to be placed in front of a headlight and providing a plurality of aligned apertures whereby to separate parallel shafts of light from said beam and permit the passage of said shafts therethrough, light intensity indicating means positioned in advance of at least one of said apertures, and light collecting and directing means arranged to receive said parallel shafts of light and to direct and focus the same onto said intensity indicating means, said light collecting and directing means being so positioned adjacent said aperture providing means that light rays reaching said collecting and directing means through an aperture in said aperture providing means are directed back through the same aperture. i

5. An apparatus for determining the direction of a headlight beam comprising means adapted to be placed in front of a headlight and providing a plurality of aligned apertures whereby to separate parallel shafts of light from said beam and permit the passage of said shafts therethrough, light intensity indicating means positioned in ing and directing means, and light intensity indicating means on the optical axis of the light collecting and directing means positioned in advance of at least one of the apertures of said aperture providing means for receiving said shafts of light focused thereon by said light collecting and directing means, said light collecting and directing means being so positioned adjacent said aperture providing means that light rays reaching said collecting and directing means through an aperture in said aperture providing means are directed back through the same aperture.

'7. An apparatus for determining the direction of a headlight beam comprising a pair of spaced diaphragms provided with aligned apertures for separatingparallel shafts of light from said beam and to permit passage of said shafts therethrough, light intensity indicating means posiadvance of at least one of said apertures, light collecting and directing means arranged to receive said parallel shafts of light and focus them onto said intensity indicating means, said light collecting and directing means being so positioned adjacent said aperture providing means that light rays reaching said collecting and directing means through an aperture in said aperture providing means are directed back through the same aperture, and means for shielding said light collecting and directing means and said intensity indicating means from the remaining rays of said headlight beam.

6. An apparatus for determining the direction of a headlight beam comprising light collecting and directing means, means adapted to be placed in front of a headlight and providing a plurality of aligned apertures arranged for selecting from said beam separate shafts of light parallel to the axis of said light collecting and directing means and for directing said shafts to said light collecttioned in advance of at least one of said d iaphragms, and light collecting and directing means for receiving said shafts of light and for directing and focusing the same upon said light intensity indicating means.

8. An apparatus for determining the direction of a headlightbeam comprising a pair of spaced diaphragms provided with aligned apertures for separating parallel shafts of light from said beam and to permit passage of said shafts therethrough, light intensity indicating means in ad vance of at least one of said diaphragms, light collecting and directing means behind said diaphragms for receiving said shafts of light and for directing and focusing the same upon said light intensity indicating means, and means for shielding the light collecting and directing means and said intensity indicating means from the remaining rays of the headlight beam.

9. An apparatus for determining the direction of a headlight beam comprising light collecting and directing means, means adapted to be placed in front of a headlight and providing a plurality of aligned apertures for selecting parallel shafts of light from said beam and for admitting them to said collecting and directing means, and light intensity indicating means disposed in advance of at least one of the aligned apertures of said aperture providing means for receiving said shafts of light from said light collecting and directing means, said light collecting and directing means being so positioned adjacent said aperture providing. means that light rays reaching said collecting and directing means through an aperture in said aperture providing means are directed back through the same aperture.

HERBERT G. HOLMES. 

